1. Field of the Invention
The invention relates to a device for the UV irradiation, in particular for the disinfection, of flowing liquids having reduced UV transmission. The device has one or more support frames with a plurality of UV modules, which each contain a mercury low-pressure radiator. The UV modules are held spaced apart essentially parallel by the support frames and extend along the flow direction of the flowing liquid, which is in particular purified waste water.
2. Discussion of Related Art
Devices of this type are in particular used in treatment plants, since nowadays the purified water from treatment plants must ever more frequently be disinfected before being discharged into natural waters. To that end, the waste water purified by the treatment plant is exposed to ultraviolet radiation (UV irradiation). The UV modules used in this case, which have mercury low-pressure radiators, generate UV radiation in the wavelength range of from about 200 nm to 300 nm with a maximum at 253.7 nm.
The UV modules are designed as UV immersible radiators and each comprise a mercury low-pressure radiator enclosed by a sleeve tube which is transparent to UV radiation. Corresponding UV irradiation devices of the type described so far are known, for example, from the documents EP 0687201, DE 3270676, U.S. Pat. No. 4,757,205, U.S. Pat. No. 5,019,256, U.S. Pat. No. 4,482,809, EP 0080780 and EP 0249450.
In contrast to clean untainted water, the waste water to be disinfected has a greatly reduced UV transmission, which is generally in the range of from 40% to 60% per 1 cm of layer thickness. This means that 40% to 60% of the applied UV radiation is absorbed by a water layer having a thickness of as little as 1 cm (for comparison: pure drinking water has a transmission in the range of from about 90% to 98%, and the absorption losses are hence only from 2% to 10% per 1 cm of layer thickness). The effect of the poor UV transmission of such media is that only relatively thin layers of the waste water around the sleeve tube can be effectively irradiated, because the efficient penetration depth of the UV radiation is so small. For layers located further away from the sleeve tube, the irradiation time needs to be long, and this necessitates a reduced flow speed. Known devices for the UV treatment of waste water can therefore only disinfect small amounts of waste water per unit time.
It is therefore an object of the present invention to permit improved UV disinfection of larger amounts of waste water having reduced UV transmission.
This is achieved in that the spacing of the UV modules from one another is selected in such a way that the cross section of the irradiation space, which is obtained for each UV module, is no more than ten times greater than the cross section of the UV module. In particular, the mercury low-pressure radiators of the UV modules should emit an irradiation strength, or intensity, of greater than or equal to 60 mW/cm2 on the sleeve-tube surface of the sleeve tube in the 200-280 nm range. The cross section of the irradiation space of a UV module is preferably no more than 7.5 times greater than the cross section of the UV module itself.
The term xe2x80x9chigh-power mercury low-pressure radiatorxe2x80x9d refers to radiators which have an electrical power of more than 150 watts per meter of radiator length and/or (in the new state) a radiation power of more than 50 W per meter of radiator length in the UV-C range. The term xe2x80x9cirradiation spacexe2x80x9d, which is obtained for each UV module, will be explained in more detail below.